Lay small 2-inch tartlet molds out on a baking sheet and lightly coat with vegetable cooking spray. Remove the dough from the refrigerator and roll it out on the counter, to ⅛-inch thickness, using flour as necessary to prevent it from sticking. Dust off excess flour and cut into 3-inch circles. Lay a dough circle over a tartlet mold and press into the mold. Trim excess dough. Continue with the remaining shells.

Preheat the oven to 350°. Cover the shells with a small round of parchment paper (just to cover), and fill the paper and shells with pie weights or raw beans to prevent the tartlet shells from swelling. Bake for 10 minutes, remove from the oven and empty out the pie weights/beans and parchment paper. Return the tartlet shells to the oven to bake for 10 more minutes.

Peel the onions and cut them in half from root to tip. Cut out the dense core at the root end and slice the onions ¼-inch thick, again from root end to tip. In a large (4-quart) saucepan over medium-high heat, cook the bacon until almost crisp, stirring often.

Add the onions, sugar, and salt, and cook, stirring often until they cook down by two-thirds, about 10 minutes. Add 2 teaspoons vinegar, reduce the heat to medium, and continue to cook until the onions are an even golden bown and softened to a marmalade consistency, 15 to 20 minutes, depending on the onions. Stir often and scrape up any brown bits clinging to the bottom of the pan. Near the end, the onions need to be stirred constantly to prevent them from sticking and burning.

Stir in the sage and kalamata olives and allow the mixture to cool slightly. Taste and adjust seasoning with black pepper and kosher salt if needed.

Preheat the oven to 350° if not still on from step 2. Stir the cream, egg and Parmesan into the caramelized onions until thoroughly combined. Divide the filling among the tartlet shells and spread evenly with the back of a spoon.

Bake in the upper third of the oven until the filling is set, about 15 minutes. The filling should still be soft but not runny. Let cool slightly and serve.